One factor which determines the quality of cotton fibers produced by a ginning operation is the amount of moisture present in the cotton lint as the lint is cleaned and ginned. Lint cleaning machines operate most efficiently, and do the least amount of damage to the cotton fibers, if the moisture content of the cotton lint is maintained within an optimum range during the cleaning operation. Cotton lint moisture content can be maintained within an optimum range by continuous adjustment of the lint drying equipment based upon the moisture content of the lint exiting the drying equipment.
A typical moisture-measurement system determines moisture content based upon the electrical resistance of the cotton. Such a system captures a sample of the cotton from the cotton flow and compresses the sample between a cathode and an anode. The system then measures the electrical resistance between the cathode and the anode. Since the moisture content of the cotton is inversely proportional to the cotton's electrical resistance, the moisture content may be calculated based upon empirically-determined equations.
Unfortunately, resistance-measurement systems tend to be accurate over a relatively small range of moisture content. As moisture content increases, resistance decreases. As a result, measurement accuracy degrades if the system cannot accurately measure small resistance values. Therefore, as moisture content increases, it is desirable to increase the resistance of the sample such as by increasing the spacing between the cathode and anode. Conversely, as moisture content decreases, the resistance of the cotton increases. This may be compensated for by decreasing the spacing between the cathode and anode which decreases the resistance through the sample. Unfortunately, this solution tends to exacerbate the high-moisture measurement problem.
Due to these disparate design concerns, typical moisture-measurement systems compromise between measurement accuracy at low-moisture levels and high-moisture levels. As a result, the accuracy of these systems is limited to a relatively small range near the center of the range of expected moisture levels. If the moisture-measurement system does not accurately determine moisture content over a sufficiently wide range of moisture levels, then a lint dryer control system tends to maintain less than optimum moisture levels in the cotton. If the lint dryer does not maintain the moisture content within an optimum range during the cleaning operation, the cotton fibers tend to sustain more damage than they would at an optimum moisture level.
What is needed, therefore, is a method and apparatus which accurately measures the moisture content of cotton over a range of moisture levels that is wide enough to provide for optimum control of a cotton lint dryer in a cotton gin.